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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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GALIANO AND BLACK GLACIERS                              89
West of the moraine which had been pushed up through the alluvial fan of 1890 is a very perfect fan built by Esker Stream. Over this the glacial waters flow in many branches which are constantly shifting (PI. XXXI). It is the most perfect alluvial fan in that vicinity, but as a perfect alluvial fan it terminates against the morainic hillocks and ridges of the buried Galiano bulb, and the waters pass down among them, making deposits in the depressions; but in 1890 the upper fan was continuous with the lower one, now destroyed. In each period of observation (1890, 1905, 1906 and 1909) the upper fan has been not only growing higher but extending laterally. The latter condition is brought out with striking clearness by reason of the fact that the alluvial fan was bordered on the north by a forest of cottonwood and spruce trees into which the glacial torrent is pouring its flood of water and sediment, burying and killing many of the trees (PL XXXV, A). Some, only slightly buried, are still growing in the barren alluvial fan; others stand there dead, and one of our packers who is familiar with the Alaskan forest, judging from the position and nature of the limbs, estimated that the gravel rose up on several of them to a height of twenty-five feet. Back in the forest were gravel terraces on which a mature forest grew, and in which, beneath the living forest, were dead mature trunks in place, proving a still older period of burial at a higher level. It is believed that these deposits were laid down when the expanded bulb of Galiano Glacier stood up as a barrier across Esker Stream, forcing the deposit of its sediment load at a higher level than at present. Thus the region has been the theatre of extensive past as well as present day changes.
The Cycle of Change. Galiano Glacier is the only instance in the Yakutat Bay region in which a practically completed cycle of change resulting from earthquake advance has been observed. It seems well, therefore, to briefly summarize the succession of events as observed and inferred.
It is inferred that at some period, long before 1890, Galiano Glacier flowed out of its mountain valley and expanded into a huge bulb extending some five miles or more from the mountains, expanding somewhat toward the west, and toward the east entering the waters of Yakutat Bay. Just beyond the mountain front was an area of clear ice, but beyond it the piedmont ice became covered with ablation moraine. Ablation proceeded to lower the surface, most rapidly in the area of clear ice, but finally reduced the entire outer area nearly or quite to sea level. A glacial stream from Atrevida Glacier, Esker Stream, built an alluvial fan up to the western side of this piedmont ice area. In the. meantime a stream, developed on the western side of the Galiano Glacier, found escape into the interior flat that had developed in the clear ice area and began to deposit there; and in this work of deposit it was ultimately joined by Esker Stream, which hitherto had been deflected southward by the expanded Galiano ice bulb. Meanwhile forest had developed on the lowered moraine to the south of the alluvial fan of the interior flat; and a growth of alder, and, toward the east, of cottonwood and spruce trees, had covered the ice bulb that still rose above the interior flat and between it and the mountain. The glacier was in this condition when Russell studied it in 1890, and when the Boundary surveyors photographed it in 1895, and doubtless continued in this condition until 1899 or 1900.
Then came the series of earthquakes in September, 1899, which shook down into the upper portion of the Galiano valley a great series of avalanches of snow and ice, the scars of some of which were easily recognizable in 1905 by comparison with 1890 photographs. Quickly, and presumably as early as 1900, judging by the age of the new alders found in